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INSTRUCTION MANUAL 

CT - 90 


Portable Frequency Counter 

• Portable battery power 

• 3 ranges 

• Gate indicator 

• 9 digit display 

• 3 gate times 


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Introduction : The CT-90 is a laboratory quality frequency counter 

that is capable of use in the lab as well as in the field. Utmost 
care has been taken in all the design stages to insure that sensiti 
vity and reliabilty were not compromised. The CT-90 has been speci¬ 
fically built for the critical user, as demonstrated by; special 
timebase options, nine digit display, three gate times, and a count 
hold feature. 

The CT-90 is ideal for portable usage. Leading zero blanking 
and the micro power oven (optional) allows 2-4 hours of continuous 
operation using the internal battery supply. 


Specifications 

Frequency Range: 2Qhz to 10 mhz (10 mhz range) 

100 hz to 60 mhz (i>0 mhz range) 

10 mhz to 600 mh/. {i»00 mhz range) 

Sensitivityi berm than 10 mv to 150 mhz 

Lomn t hau I M) mv to 600 inhz 


Resolution: 

Input Impedance: 
Input Protection: 

Time Rase: 


Display: 

Power: 

Size, weight: 


0.1 hz (10 mhz range) 

1.0 hz (60 mhz range) 

10.0 hz (600 mhz range) 

1 meg ohm, 33 pfd (10 and 60 mhz) 

50 ohms (600 mhz) 

10 find 60 mhz rangu; 150 vac to 
10 mhz , 50 vac to 60 *mhz. 

600 mil/, range; 5 vac 

10.0000 mhz; 

Standard time base- temperature 
compensated TCXO- 1.0 ppm 2Q°-40°C 
High stability, proportional controlled 
micro power oven option (OCXO)- 
0.1 ppm 20°-30°C 

9 digit, 0.4" height 
automatic decimal placement 

8-15 v AC/DC at 250 ma max with TCXO, 
300 ma max with OCXO, 4 ’AA* size 
nicad batteries 

5" x 5" x IV, 1 pound with batteries 


1 









Operation; Operation of the CT-90 is very simple, simply connect your 
input signal to the proper input jack (10, 60 mhz or 600 mhz) and 
select the range and gate time. All switches, except the external 
time base switch (optional) are mounted on the front panel in easy 
view of the user. A description of the front panel controls follows. 

POWER: OFF turns the counter off 

ON turns the counter on 
HOLD stops the clock signals to the 
counter circuits and holds the count 
that is displayed. 

GATE t 0.1 sec position selects a one ...tenth 

second gate period. The gate period 
is the time interval over which input 
pulses are counted. The faster gate 
period allows a faster updated count 
at the expense of less resolution. 

1.0 sec position selects a one second 
gate period. This position is used 
when better resolution is required. 

10 sec position selects a ten second 
gate period. This position is used only 
when extreme accuracy i‘< rmpiittid .uni a 
long term, ■table ihjuiJ «vaJ Uhlis 

RANGE: 10 mhz position is used when input sig¬ 

nals are connected to the 10, 60 mhz 
input jack. The counter will then count 
up to 10 mhz with 0.1 hz resolution. 

(10 sec gate) 

60 mhz position is used when the input 
signals are connected to the 10, 60 mhz 
input jack. The counter will then count 
up to 60 mhz with 1.0 hz resolution. 

(10 sec gate) 

600 mhz position is used when the input 
signals are connected to the 600 mhz 
input jack. The counter will then count 
up to 600 mhz with 10 hz resolution. 

(10 sec gate) 

GATE LIGHT: Indicates when the counter is actually 

measuring input signals. The gate light 
gives a visual indication of gate time 
and counter operation. It is extremely 
useful when using the longer gate times. 


ASSEMBLY DIRECTIONS 

Construction Notes:Use a small tipped iron for assembly. A oower 
rating of 30-50 watts is ideal. Do not use a soldering guni Do 
not use any sort of additional solder flux, use only a good grade of 
rosin core solder. Proper soldering techniques are important! Each 
joint should be shiny and completly surround the lead wire. There 
should not be just a slight dab of solder barely held on to the lead. 


2 




















ASSEMBLY DIRECTIONS (continued) 

Don't be afraid of damaging a component due to too much heat, 
modern day semiconductors can withstand more heat than your iron can 
put out! Use enough heat to form a good solid joint, a quick touch 
of the iron is usually not enough. The main PC board has plated thru 
holes, thereby eliminating the need to solder top side of the board. 
This, however, makes removing a part more difficult, so follow the 
directions closely. Keep component lead lengths as short as possible. 
Note that components in the U4,U1 and U2 area must be kept close to 
the PC board so that the battery holder can be mounted above them. 

Review all assembly details before beginning construction. 

Assembly: 

1) Locate the main counter PC board and install the 28 pin socket 
for U3, the two 16 pin sockets for ul and U4, and the 14 pin 
socket for U2. 

2) Install CJ, C 4 and C5* All .03. Do not Install Cl at this 

l i me. 

3) Inst a 1 l t‘6 ( 1 00 pH and Cl 2, .01 

4) (natal.I c /, ch, n, CIO -md c llj .22 to 10 ufd. Noto the po** 

l.nity on 'll llmtio C(i|irti’ltori. 

5) inn Util CKl t ht u ( IN414H type ftm.i 1 I glass signal diodes. 

Note polarity. 

6) Install CR8 thru CR14; 1N4003 type, 1 amp diodes, observe polarity. 

7) Install al r R20, R21, R22, R24, R26, all 10K ohm. 

8) Install R2, R10, Rl2, Rl3, and R14, R23, all 470 ohm. 

9) Install jumper where R3 is located. Use scrap component lead. 

10) Install R4; 100 k ohm,and R5| I meg ohm. 

11) Install R6, R9 , Rli and R25? all 1 k ohm. 

12) Install R7, R15, Ml fi and IU 71 all 270 ohm. 

13) Install Rflj ISO ohm, Rrart color coding carefully. 

14) Install R18 ami M2H ; both 100 ohms. 

15) Install Ql| MRF502 , Q2j 2N54H4, Ql and 04; 2N5771, QSj 7545 and 
Q6; 7546* Note the positioning of these transistors before In¬ 
stalling. Keep the 1m, ids ol 04 ami 0* short SO that I Im tot al 
height of each part does not exceed 3/B" . 

16) Install VR-1 ; 7805 voltage regulator. Bolt the regulator to 

PC board before soldering using (1) 4 4(1 x V screw and nut. 

17) Install C15; 1000 ufd and C16; 220 ufd. Be sure both parts are 
seated against PC board. Note polarity. 

18) If you are going to use the standard I ppm t ime base follow steps 
19 thru 21. If you are going to use the micro power 0.1 ppm 
oven proceed directly to step 22. Be sure to read all instruc¬ 
tions given with the micro power oven, 

19) Install C14 and C17. These part values are matched to the crystal 
used and may vary. See parts list. 

20) Install R19; 22 meg ohms.and Cl3; trimmer capacitor. 

21) Install Yl? 10.000 mhz crystal. Note: When using the standard 
1.0 ppm crystal time base, diode CR7 is not used. Proceed now 
to step 24, ignore steps 22and 23, 

22) Install the precision oven oscillator module as shown in dia¬ 
gram. Be sure the module is aligned properly and seated firmly 
against PC board. Note that there are no parts installed or 
supplied for R19, C13, C14, C17 or Yl. 

23) Install CR7 as shown. Note, CR7 is used ONLY with oven option! 

24) Install ul; 11C90, U2; 74196, U3; 7216 and U4; 10116 IC's. Be 
sure that the IC's are installed in the correct sockets and that 
they are not installed backwards. Are all the IC leads inserted 

3 




24) 


It is very easy to have some leads bent under 


25) 

26) 

27) 


23) 

29) 


30) 


into the socket? 
the IC body. 


Set the main PC board aside and locate the read out board. 
Carefully examine the readout PC board for any shorts between 
lands that could have occured in manufacture. The R.E, symbol 
marks the solder side. 

Install the nine readouts (DS1 thru 9). Note the position of 
the ridges on the top of the readouts. Seat all readouts firm¬ 
ly against the PC board. Be fore soldering be sure they are lined 
up straight and even. Note that the readout board has many 
fine PC traces and requires much care in assembly. Inspect 
each joint after soldering for any possible bridges. It is much 
easier to find mistakes now, as troubleshooting of solder bridges 
is quite difficult. Do not rush this portion of assembly 1 
Install CR15; Red LED as shown. Be sure that the long lead is 
installed in the bottom-most hole. 

Install the three slide switches as shown in layout. Be sure 
the switches are seated all the way and that the guide pins are 
inserted in their holes in the PC board. If the switches are 
not seated correctly, they will cause assembly problems later. 
Note that the connections that have to be soldered are very 
small and close together. Care must be taken not to cause any 
solder bridges. Do not cut the switch leads afte r soldering. 

The readout board mounts at a right angle to m uii b mid 

with solder pads and switch loads pioViilinq both mn« 
support and electrical connection between 1 he two boards. The 
readout board is placed against the main board so that Hit* Holder 
pads on the readout board line up with the solder pads on the 
main board. Note that there are two sets of pads on the readout 
board. One set connects to the top of the main board, the other 
set to the bottom (solder side) of the main board. Solder the 
bottom row of the readout pads and switch leads flush with main 
board between the pads on the readout board. Check to be sure 
the two boards are perpendicular and not tilted, then solder 
all remaining pads. Use enough solder to provide a good mechan¬ 
ical connection, but don't cause any solder bridges between 
adjecent pads. 


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31) Locate R27; 15 ohms. One lead of this resistor mounts on the 
main board and the other end connects to the read out board 
at the extreme end. This resistor, therefore stands upright. 



32) Locate the two conductor strip cable and install both leads at 
one end to the holes marked 'AC. The other end will be connect¬ 
ed later. 

33) Locate the battery holder assembly and solder the black and red 
leads to the holes labeled 1 BATT'. (red to plus) 


4 























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34) 


35) 

36) 

37) 

38) 

39) 

40) 

41) 

42) 

43) 


44) 


45) 

46) 

47) 

48) 

49) 


Note the location of the battery holder mounting holes and po¬ 
sition the battery holder over VR-1 so that the red and black 
leads face toward the front of the counter (toward readout board). 
Note which holes in PC board line up with mounting holes in 
battery holder. 

Install the two 3/8" standoffs on the componet side of the PC 
board in the holt's that line up with the battery holder. Use 
two 4-40 x 3/16" screws. Posistion standoffs so they don’t short. 
Mount the battnry holder to the top of the standoffs using two 
4-40 x 3/16" screw;;. Be sure not to damage any parts under the 
battery holder. The two conductor cable from the ’AC 1 holes 
should extend nut to the rear. 

Locate the bottom housing, (the half with the two holes) 

Locate the font rubber feet, peel off the protective paper and 
mount them m the four corners of the outside bottom cover. 

Slide the front panel into the grovrs provided on the bottom 
hOUSJ i n<i. 

Place the mm in PC bti.iiil into Hie bottom housing no that the 
three elide uwlltiie?* extend IliiU the uwitch holes in the front: 


plate. 

Mount the pc board using the fout 4-40 screws. Do not overtighten. 
Locate the rear panel and mount the miniature phono jack to 


the center hole. 

Mount the two BNC connectors 
lug under each nut. 


to the rear panel. 

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Install a solder 




soaa-ft too* 


Solder the two romalning loads from the cabls connected to the 
*AC' holi'H to tin* phono jack a;t shown: 





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Slide the rear panel into the rear slots of the bottom housing. 
Locate Cl? .01, connect one lead to the center of J1 and the 
other lead to the PC land that connects C2, CRl, and CR2, Keep 
the leads as short as possible. You may wish to remove the 
battery holder while doing this. 

Using a scrap component lead, connect the ground lug of Jl to 
the ground plane of the PC board. Keep this lead a short as 
possible, 

Connect a scrap component lead from the center of J2 to the pad 
on the main PC board labeled J2, Keep this lead as short as 
possible. 

Connect a scrap component lead from the solder lug of J2 to the 
PC board ground plane. Keep this lead as short as possible. 


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5 








50) Locate Cl8; 22 pfd. Connect one lead to the center of J2 and 
the other lead to the PC board ground plane. Keep leads as short 
as possible* 

51) Locate the red lens and place it between the readouts and the 
front plate* 

52) The unit is now ready for checkout and calibration (note: the 
precision oven option does not require calibration, it is factory 
calibrated), 

53) If problems occur see the trouble shooting hints and theory of 
operation. After calibration the top cover can be installed 
using the two phiHips head screws. Do not overtighten. The 
cover will only mount one way. 

Calibration: 

1) If nicad batteries are to be used, be sure they are fully charged 
before attempting to calibrate the counter, 

2) Connect a signal of known accuracy to the counter input, A 100 
khz calibrator which has just been zero beated to WWV or the 
CB-1 color burst adaptor works well* 

3) Set the gate time to 1.0 seconds and adjust C13 until the dis¬ 
play shows the proper frequency. 

Theory of Operations: 

General: Regardless of the type or complexity of a frequency counter, 

all instruments measure frequency by counting input pulses with res¬ 
pect to a known frequency or time base. The time base generates a 
precisely controlled time interval, selectable to be one second or one 
tenth of a second. During this period, the counter is enabled and in¬ 
put pulses counted. When the time period is up, the number of pulses 
counted is then displayed. A long gate period allows more pulses 
to be counted, and the more pulses counted the better the resolution. 
The limiting factors governing resolution are the number of digits 
in the display and the tolerable gate period. Usually 1.0 hz is the 
best resolution practical for an easy to read updated count. Of 
course it is not always necessary to read frequency to a hertz or 
wait for a one second count. By selecting a shorter gate period', 
you can reduce the display update time and get a faster reading dis¬ 
play, but at the expense of poorer resolution. 

Detailed Theory; The UHF and VHF inputs have been kept separate to 
increase the input sensitivity by eliminating switching losses* The 
UHF signals are feed thru Jl, past CR1-CR2 input protection diodes 
to Ql, the first amplifier/limiter stage* The signal is then sent 
to Ul, divide by ten IC. 

The VHF input is much different because it must be of a very 
high impedance. The signal is feed thru J2, past CR3 and CR4 input 
protection diodes to the gate of Q2; FET. The combination of the FET 
and Q3 bootstrap bipolar transistor follower provides the high imped¬ 
ance required. The signal is then sent to the three stage line amp 
U4* This IC is an ECL device that limits and shapes the signal* 
Transistor Q4 then converts the ECL level to a TTL level signal that 
the rest o f the counter requires* The input to U2 divider is selec¬ 
ted by the range switch. 


6 







B4 


4 


Its input can come from the UHF section (U4) or the VHF section (Q4). 

If the 10 mhz mode has been selected U2 is bypassed completely and 

the signal is sent directly to U3, the counter IC. 

The timebase for U3 can be supplied by Y1 and its associated 
components or by an external timebase. The counter IC will use which 

ever timebase that has been selected at pin 1. If CR7 is installed, 

the timebase connected to pin 24 will be used. The counter IC gen¬ 
erates all its own housekeeping functions such as multiplex, strobe, 
gate and reset signals. A logic circuit inside the counter IC senses 
the scanned readout signals (DO thru D7) and also the input to pin 14 
the gate select input. By comparing these inputs, the counter IC 
generates the selected gate time. The decimal point is displayed 
the same way. A logic circuit inside the IC looks at the scanned 
outputs DO thru D7 and compares this with the signals selected by S2. 

The power nupply uses a simple bridge rectifier circuit that 
will accept an AC or DC input. Regulator VR1 provides a stable 5V 
powi^r source* wh 11 o R28 and CH12 provide thv charging current for the 
nica&rt (it unod) . Capacitors <' 1 '* mid C H» provided added filtering. 


Trouble Shoot lug H 1 nl '> Th* ( i i l '. I - ■ i * involved in tioublf ft hooting 
in t o carefully examine a i i ynm wni k, chock parts placement against 
parts lint and l*c layout. M.ike sure all diodes, transistor**, fC'o 
and capacitors are orientated correctly. Above all, check all solder 
connections I Examine all PC runs to verify that no solder bridges 
exist. Carefully check the readout board as it has quite a few close 
foil runs. 

PROBLEM: Entire display does not light? 

Check: Power supply voltages, connections to readout 

board, solder bridges across power switch and correct 
external nupply (if used). Also check the timebase 
circuit lined. tl the counter lacks a timebase input 
l hi* display may blank. 


PROBLEM: 

PROBLEM: 

PROBLEM: 

PROBLEM: 

PROBLEM: 

i PROBLEM: 


%V not pr Ment 

Check: CRH thru CRM, VH I and bnltriry holder assem¬ 
bly. Check for shorts on the w buns. Arc any ic’s 
inserted backwards? 

Display lights but shows odd characters 

Check: All solder joints on readout board- Look 

closely for bridges. 

Digit not lit 

Check; U3, be sure all pins are seated properly. 
Check PC traces connecting pins 1 and 6 of readout. 
Segment not lit in all digits 

Check: U3, Be sure all pins are seated properly. 

Check PC traces to readouts for shorts and open con¬ 
nections . 

Only one digit lit. 

Check: Timebase circuits, connections to pins 1 and 

6 of lit readout. Also look at power supply voltages 
Display flickering. * 

Check: Power supply voltages. Note that when unit 

is used for extended periods from AC adapter, some 
power is used from batteries (nicads only). A full 
charge can only be provided when the power switch 
is in the off position. 


7 


PROBLEM: 


PROBLEM: 

PROBLEM: 


No gate light* 

Check: Timebase circuits, Q6 and solder pads at the 
junction of the readout board and main board. Is 
the power switch in the hold position? 

No decimal points. 

Check: Q5,R27 and S2 connections. 

Only some digits are lit. 

Check: Input signal. This unit has leading zero dis¬ 
play blanking. The digits before the decimal point 
will not be turned on until a signal is applied. 


HOW TO USE YOUR COUNTER 


Using your counter is usually just as easy as connecting the 
signal to the input jack and counting. However, in some instances, 
such as noisy signals or low frequencies, care must be taken in apply¬ 
ing the signal to the counter. The counter not only has a high input 
impedance but also high sensitivity. Noise accompanying the desired 
signal may fall with in the counter's sensitivity and frequency limits, 
and be counted. This signal plus noise input is amplified and counted 
within the instrument, and produces a jittery, unstable display. 

The solution to this problem is to attenuate the signal plus noise 
to the level where the noise is below the counti’i Lhrmihold A scope 
X1G probe is ideal fot this purpose, an easily constructed probe of 
this type is described later on. 

Another problem area is ringing at the counter input. Consider 
the coax cable from the signal to be measured to the input jack, 
it f s a transmission line, just like your antenna coax on a transmitter. 
Being so, a standing wave phenomenon* can occur if impedances are mis¬ 
matched. If a signal from a low impedance source is presented to the 
coax cable, and the cable is connected to the high impedance counter 
input, the signal will be mismatched. This mismatch will cause the 
signal to reflect from the input and return, causing again, an unstable 
display, 

Yet another consideration is that of ground loops. If your 
counter probe is grounded to the circuit to be measured, and the counter 
case also grounded (whether physically or induced) a ground current 
along the cable can exist. -This ground current will produce a voltage 
which, if it is AC, will be counted. 

Fortunately, most of these problems are easily solved by thought¬ 
ful selection of coupling the input signal. This involves determing 
just what sort of signal you are attempting to measure. 

For Low Frequency (less than 20 khz) Measurement: Low frequency 
measurements are usually upset^by excessive noise riding on the input 
signal, ground loops or ringing. Even though you may feel the signal 
is very "clean”, the counter can count up to VHF and noise or ring¬ 
ing will be counted. The use of a low pass filter will prevent any 
high frequency noise or ringing to be presented to the counter input. 
Preventing a ground loop is not quite as easy as using a different 
probe. Generally, providing a ground path other than the probe's 
ground will solve the problem. Two simple low pass probes are shown: 


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For General Usage { 20 khz to 60 rnh 2 ) Measurement: The majority of 
signal measurements are usually within this range. Ringing and 
noise are the chief culprits in measurement. The only way to counter* 
act these undesirables is to damp the ringing and/ or attenuate the 
noise (with the signal too, unfortunately). A simple X10 oscillo¬ 
scope prob»- wrirkti well to attenuate noise an well as providing a less 
loading probe. ll the noise is at a 10 mv level and signal at 1 volt, 
the X10 probe will reduce the noise to I mv and the uignal to 100 mv, 
thus I he imt'ii' is mil ol t:hn ocnint«*i t *.i sennil ivil y range, while the 
deni led signal inn 1 I The XI0 piobi ni high impedance pi oho will 
ii.l tin (jt “iif ■ i .i I I y d.imi * mil r mi« ling. Andlir-i h'-m-lil ot the high imp'' 
dams; probe im that il dotstui' l load l he enroll being measured ljy 
the input cable's capacitance. This in especially important when 
measuring oscillators or amplifiers. A simple high impedance probe 
is shown below: 





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For Direct Transmitter Measurement : Measuring a transmitter i i»|uJ res 
coupling enough transmitter energy into the counter for a stable 
count and not so much as to exceed the counter's safe input. Gen¬ 
erally, for VHF work, a small 18" whip antenna will pick up a trans¬ 
mitter from 5 to 10 feet away. Direct connection to the transmitter 
can be made via a coupling box or pick up loop. The pick up loop 
is simply a few turns of wire wrapped around the transmitter's antenna 
coax and fed to the counter. The coupling box requires breaking 
into the transmitter's antenna coax. Schematic is shown below: 


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FREQUENCY COUNTER ACCESSORIES 

CT-90 110 vac power adapter 
CT-9G Nicad battery pack and adapter 
CT-90 External power cable# 8-15 VAC/DC 
DC Probe, direct input 

High Impedance Probe, low circuit loading 
Low pass Probe, for audio measurement 
High Pass Probe, reduces low freq pickup 
Collapsible whip antenna {20 inches) 

CB-1 Color Burst Adapter for calibration, 
high accuracy, typically ,QOlppm 
PS-2 Audio scaler, multiplies audio wired 

signals times 10 or 100, gives kit 

0.1 or 0.01 hz resolution with 
1 sec gate 

OSC-1 Micro power proportional controlled 

oven- increases stability to 0.1 

ppm, 20-30° C, factory wired and calibrated. 
External Timebase input Conversion Kit 

Allows connection to external time- 
base ,includes BNC connector, switch, 
electrical parts needed and new 
rear panel 


WARRANTY 

All parts used in the CT-90 counter are warranted to be free 
from any defects for a period of 90 days. Parts found to be defective 
within this period will be replaced promptly without charge upon 
receipt for inspection at the factory After the warranty period 
has passed, parts may be purchased per the price list. Ramsey Electronics 
cannot be held responsible for faulty workmanship during assembly 
or damage/harm caused by construction or installation errors. 

Units obviously misused or modified are not covered by this warranty. 

REPAIR SERVICE 

Assembled CT-90 kits may be returned for repair and calibration 
to factory standards for a fee of $20.00. This fee covers repair, 
calibration, shipping, insurance, handling and a service report on 
difficulties found. CT-90 units assembled with paste flux, acid core 
solder or soldering guns will not be accepted. Ramsey Electronics 
reserves the right to refuse repair on unreasonably constructed units. 

Pack all returns adequately and insure for your own protection. 


10 







CT-9 0 PARTS LIST 


DESIGNATOR 


Cl thru C5 
C6 

C7 thru Cll 
C 12 
C13 

1S5S1, Cl7 
C15 
C16 

cie 

CRl thru CR4.CH6 
CR7 

CR8 thru CR14.CR5 
CR15 

DSl thru DS9 
Jl, J2 
J3 
Q1 
Q2 

Q3, Q4 
Q5 
06 

Rl,R20thru RZ2 R24, R26 10 k ohms,Brn-Blk-Org 

R2 ,RlO,Rl2, R13, RM.R23 470 ohms, Yel-Vio-Brn 
r 3 Jumper wire 

R4 loo k ohms, nrn-Blk- Yel 

RS 1 Meg olunn, Urn-Blk-Grn 

R6, 119, Rll, R25 I K olunn, Urn-Ulk-Rod 

U7, R15, u 1b, rnzm, 270 uhm», Rod Vlo-htn Ain *1 K oh vn 

t SO ohimi, Min I Ml Bin 
100 olumi f Bj n HI k Hi n 
22 moq oliiiui, I{t* 1 1 ItC'd DlUo 
(STD OSC only) 

15 ohms. Urn nrn Hlk 
Slide switch, J position 
llc90, High speed decade 
prescaler IC,8680 
74196, TTL decade counter 
7216, MOS, LSI counter 
10116, ECL Amplifier 
7805, voltage regulator, 5V 
10.0000 Mhz crystal 
Non- Referenced Items 
Socket Set 1-28 pin, 2-16 pin, 1-14 pin 
CT-90 PC board 
CT-90 Display board 
Hook-up wire, 4"- 2 conductor 
Phillips head screws, 1", Qty 2 
Solder Lug, 3/8" hole size, Qty 2 
Rubber feet, strip of four, pressure sensitive 
Red lens, 4 V* x 3/4" 


R8 

RIB, R28 
R19 

R27 

SI, S2, S3 
U1 

U2 

U3 

U4 

VR-1 

Y1 


DESCRIPTION 

.01 uf disc ___ 

100 pf disc 
1 to 10 uf 
10 uf 

4-40 pf (used in std TB) 

22 pf CIA 30 Pf disc 

1000 Uf, 16VDC 

Ion Uf, 16VDC ti 3 

IN4148type, small signal diode 
lN4140type, (optional Time base) 

IN400 H ype,) amp power diode 

LED, Mini ied 

FNt) i9, Readout 

HNt* connori or 

Mnli mi n i .ti ut e phono 

MRF502, NI'N 1 i amt l nI Or ,2N5179 

2N5484, FET 

2N5771, PNP transistor ,2N4258 
NPN, 2N3904 type 

PNP, 2N3906 type 


11 







DESIGNATOR 


DESCRIPTION 




Non-Referenced Items 


4-40 x * screws* Qty 5 
4-40 x 3/16” screws, Qty 4 
4-40 x 3/8” standoff, Qty 4 
4-40 Nut, Qty 1 

CT-90 Housing, ABS Plastic, top and bottom 
CT-9 0 Front panel, punched, labeled 
CT-90 Rear panel, punched 
Battery holder, 4-AA cell type 


INTERNAL OPTIONS 

OSC-1 Micro power, proportional controlled oven 
Factory calibrated, 0-1 ppm 20-30°C 
External timebase input conversion kit 





12 







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CT-90 REVISIONS 


1. Enclosed phono jack may look like: (J3) 


NO 


-g 



or 



Ac iNP^r 


Fi c Yn tor* 

Side View 


AC'Thput Rear View 


2. Be sure stand-offs (step 35) do not short 5 volt trace to ground. 

3. 05 is drawn backwards on layout. Should be: 



4, R23 is 470 ohms. 

5. In step 34, red and black leads may not face forward. 

6 » * ?; ia°nf 

7. C12 changed from .01 to 10 uf. 

8. CR-5 changed from IN914 to IN4003, 

9. ±* upf . All is $ c> Wm 

AlTACH^D 12/lC 

T& f>wCOvA- AlOfc ,